The U.S. Senate is headed toward a possible vote on a $900 billion version of an economic stimulus bill aimed at stopping the U.S. economic decline. President Obama said failure to quickly approve the measure would be irresponsible, as he continued to step up pressure on minority Republicans opposing the legislation.

Lawmakers have engaged in some of the fiercest debate heard in years on the huge spending and tax cut proposal, working through numerous amendments from both sides of the political aisle.

With spending on domestic programs, the aim is to pump hundreds of billions of dollars into the U.S. economy to jolt it out of a deepening recession.

Democratic leaders are trying to assure at least 60 votes required to approve the measure and avoid any procedural roadblocks put up by Republicans.

Majority Leader Harry Reid voiced optimism for a late Friday vote, as he appealed to both parties to support President Barack Obama on the stimulus measure.

"President Obama is taking responsible steps that we need to begin the long road to recovery," Reid said.

But overcoming partisan differences has been difficult, as Republicans assailed what they called wasteful and unfocused spending they said threatens to sink the American economy in deficits and debt.

"Republicans are ready to support a stimulus bill, that really hasn't been in question. But we will not support an aimless spending spree that masquerades as a stimulus," the senator said.

Republicans John McCain and Lindsey Graham criticized behind-the-scenes negotiations in which moderate Republicans and Democrats were attempting to forge a compromise, saying anything emerging from the talks would not be bipartisan:

"Just picking off a few [Republican] votes is not going to solve our nation's problems," said Graham.

"You cannot call a bill bipartisan if it has two or three or four or even five Republicans out of 535 members of Congress. You can call it an agreement but you cannot call it a bipartisan agreement," McCain added.

One Democrat, Diane Feinstein, said she was growing increasingly concerned about stimulative impact of the bill. "I reserve the right at the end of the day to vote against the package that I don't think puts those jobs out there," she said.

However Democrat Debbie Stabenow, from Michigan, with the nation's highest unemployment rate at 10.6 percent, said the bill signifies a turn away from policies of the past:

"We have seen those policies in place, we have seen the results of those, and they didn't work," Stabenow said.

The latest U.S. jobless figures featured prominently in Senate debate throughout the day Friday.

Lawmakers from both parties cited figures showing U.S. unemployment climbing to its highest level since 1982, with nearly 600,000 jobs lost in January, and a 7.6 percent national jobless rate.

President Obama said Friday that failure to approve the bill would be inexcusable and irresponsible.

"They (the electorate) did not vote for the false theories of the past and they didn't vote for phony arguments, and petty politics. They didn't vote for the status quo, they sent us here to bring change, " the president said, speaking late Thursday to House democrats in Williamsburg, Virginia.

Republicans in the House of Representatives issued a statement Friday expressing disappointment with what they called the president's abandonment of his previous calls for bipartisanship.

House Republicans withheld all of their votes from a separate $819 billion version of the economic legislation, and they have urged Senate Republicans to reject the version in that chamber of Congress.